430 X. GENEEAL REJIARKS. 



more widely separated spaces, the floral diversity be- 

 comes correspondingly wider ; far the greater number of 

 the Vectian species being unknown in the northerly 

 group ; and several of the Orcadean species being in 

 turn absent from the southern isle. 



But if we set Orkney against Scotland ; that is, a small 

 space against a much larger tract, we shall then find all 

 the species of the small space repeated in the larger tract, 

 along with numerous additions. The diversity here is 

 entirely negative for the Orkney flora, and of course 

 entirely positive for the Scottish flora. A considerable 

 amount of floral identity remains amid the diversity; 

 that is, all the certain species of Orkney are identical 

 w^ith some among those of Scotland. A submergence of 

 the entire gi'oup of Orkney Isles would not deduct a 

 single species from the British flora. This would not be 

 quite the case with the more distant Shetland group ; two 

 seeming species, or strongly marked varieties, being found 

 in Shetland, and not elsewhere in the British Isles. 



Enlarging upon the last comparison, the smaller ad- 

 jacent island of Ireland may be set against that of Britain 

 proper. Nearly the whole flora of the former is found 

 repeated in the latter ; the small exception in the Irish 

 flora constituting its positive diversity, and not counting 

 up to a score of clearly admitted species. But the flora 

 of Britain, the larger tract, includes some hundreds of 

 species which have not been seen truly wild in Ireland. 

 This diversity, it should be noted, is not at all confined 

 to the species of North Britain, which is situate out of 

 Irish latitudes. 



Again rising to larger tracts, a similar comparison may 

 be made between Britain and Europe. It has been stated 

 before, that there are extremely few certain species of the 

 former, which do not occur somewhere in the latter ; 



